VLF INTERMEDIATE DISTANCE PROPAGATION

VLF phase transition onset of signals transmitted from Golfo Nuevo, Argentina (430 S, 6S W) and recorded at Atibaia, SP (23 S, 43 W) were analized. The onset of the phase transition when passing from dusk to dawn, with respect to the ionizing Lyman-a radiation, indicates the onset of the ionization in the D-Layer of the ionosphere. The data analyzed from 1977 to early of 1980 show a well defined sunrise time annual variation.